Lectin binding of F9 embryonal carcinoma cells: evidence for population heterogeneity and developmentally regulated high–Mr cell surface proteins

Abstract

Undifferentiated F9 embryonal carcinoma (EC) cells bound fluorochrome-coupled Helix pomatia agglutinins (HPA) and peanut agglutinins (PNA) homogeneously, but were distinctly heterogeneous in their binding of Dolichos biflorus agglutinin (DBA) conjugates. Upon chemically induced differentiation the proportion of cells binding the DBA conjugates increased, but a distinct heterogeneity in the intensity of binding remained among the parietal endoderm (PE)-like F9 derivatives. These cells were heterogeneous in their binding of HPA conjugates as well, and many of them failed to bind PNA conjugates, apparently due to sialylation of the PNA-binding sites. Electrophoretic analysis of lectin-binding glycoproteins in the detergent-soluble fraction of the cells revealed the appearance of a doublet of polypeptides of Mr 300,000-400,000 upon differentiation induced by retinoic acid (RA). In addition, an Mr 220,000 polypeptide appeared upon differentiation induced by RA and dibutyryl cyclic AMP (dbcAMP). These polypeptides were obtained from both metabolically labelled and surface-labelled cells. A major secreted glycoprotein, which comigrated with laminin, bound to DBA. This suggests that laminin secreted by the differentiated F9 derivatives contains O-glycosidic saccharides. The results show that even though differentiation of F9 cells leads to changes in their binding of fluorochrome-coupled lectins, these lectin conjugates reveal distinct population heterogeneity among undifferentiated and differentiated F9 cells and are hence likely to be of limited value in the characterization of individual cells. At the whole cell population level, on the other hand, affinity binding to lectins reveals the appearance of high-Mr cell surface proteins in differentiating F9 cells.